Optimisation of the diagnostic strategy for suspected deep-vein thrombosis in primary care

Summary

Recently, a diagnostic score was developed to safely exclude deep-vein thrombosis (DVT) in primary care. A large prospective study, in which general practitioners used this diagnostic score to decide which patients needed referral, revealed that the number of referrals for ultra-sound measurements was reduced by almost 50%, at the cost of an acceptably low risk (1.4%, 95% confidence interval [CI] 0.6% to 2.9%) of venous thromboembolic events in non-referred patients. However, simple adjustments to the diagnostic score (so-called updating) might further improve the accuracy; i.e. reduce the proportion of missed diagnoses (safety) or increase the proportion of patients who do not need to be referred (efficiency). We applied two updating methods to determine whether adjusting the weights of the predictors or adding new predictors could further improve the accuracy of the diagnostic score. The weights of the predictors did not need to be adjusted, but inclusion of ‘history of DVT’ and ‘prolonged travelling’ significantly added predictive value (p-values 0.014 and 0.023, respectively). However, adding these predictors to the diagnostic score did not improve the safety and efficiency: at equal safety (1.4% missed diagnoses among the non-referred patients), the efficiency was lower (43.5%, 95% CI 40.4% to 46.6% compared to 49.4%, 95% CI 46.3% to 52.5%). The diagnostic score for excluding DVT in primary care has good accuracy in its original form and could not be improved by including additional predictors. This suggests that the original diagnostic score can be used to safely exclude clinically suspected DVT in primary care.

Keywords

Deep-vein thrombosis - diagnosis management - epidemiological studies

• References

• 1 Oudega R, Moons KG, Hoes AW. Ruling out deep venous thrombosis in primary care. A simple diagnostic algorithm including D-dimer testing. Thromb Haemost 2005; 94: 200-205.
• 2 Toll DB, Oudega R, Bulten RJ. et al. Excluding deep vein thrombosis safely in primary care. J Fam Pract 2006; 55: 613-618.
• 3 Oudega R, Hoes AW, Moons KG. The Wells rule does not adequately rule out deep venous thrombosis in primary care patients. Ann Intern Med 2005; 143: 100-107.
• 4 Buller HR, Ten Cate-Hoek AJ, Hoes AW. et al. Safely ruling out deep venous thrombosis in primary care. Ann Intern Med 2009; 150: 229-235.
• 5 Janssen KJ, Moons KG, Kalkman CJ. et al. Updating methods improved the performance of a clinical prediction model in new patients. J Clin Epidemiol 2008; 61: 76-86.
• 6 Steyerberg EW, Borsboom GJ, van Houwelingen HC. et al. Validation and updating of predictive logistic regression models: a study on sample size and shrinkage. Stat Med 2004; 23: 2567-2586.
• 7 Janssen KJ, Donders AR, Harrell Jr. FE. et al. Missing covariate data in medical research: To impute is better than to ignore. J Clin Epidemiol. 2010 prepub online.
• 8 Rubin DB. Multiple Imputation for Nonresponse in Surveys. Hoboken, New Jersey: John Wiley & Sons; 1987
• 9 Schafer JL, Graham JW. Missing data: our view of the state of the art. Psychol Methods 2002; 07: 147-177.
• 10 Rathbun SW, Whitsett TL, Raskob GE. Negative D-dimer result to exclude recurrent deep venous thrombosis: a management trial. Ann Intern Med 2004; 141: 839-845.
• 11 Wells PS, Anderson DR, Rodger M. et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med 2003; 349: 1227-1235.
• 12 Toll DB, Janssen KJ, Vergouwe Y. et al. Validation, updating and impact of clinical prediction rules: A review. J Clin Epidemiol 2008; 61: 1085-1094.